Wireless local area networks (WLANs) and mobile communication devices have become increasingly ubiquitous, such as smart phones, wearable devices, various sensors, Internet of Things (IoTs), etc. With its overall size constrained by portability requirements, such a communication device typically is powered by a built-in battery of limited charging capacity. Most workloads of a communication device can be communication-driven and therefore the wireless radio is a major power consumption source as it needs to remain operational to ensure prompt responses to data communication requests.
To reduce power consumption by the wireless radios, some communication devices include a main radio and a low-power wake-up radio (WUR). When it is not involved in data communication tasks, the main radio can be placed into a power conservation state, e.g., a sleeping mode or even turned off. On the other hand, the low-power wake-up radio (WUR) remains active and operates to activate the main radio whenever the WUR receives a data communication request that is directed to the main radio, e.g., in a form of a wake-up signal transmitted from a WI-FI access point (AP).
Compared with a main radio with high rate data communication capabilities and complex processing functions, a WUR is a low-cost and low power consumption radio and yet suffices to receive and process a wake-up signal and accordingly activate the main radio. For example, the nominal power consumption of a WUR can be 0.5-1 mW or even less.
The Institute for Electronic and Electrical Engineers (IEEE) 802.11 family specifies technical standards for WLANs. The latest generations of IEEE 802.11 standards adopt multi-user (MU) communication schemes, such as Multi-User Multiple-Input Multiple-Output (MU-MIMO) and Orthogonal Frequency-Division Multiple Access (OFDMA). However, there is lacking an MU transmission mechanism that enables simultaneous wake-up signal communication between a transmitter and multiple WUR receivers.